Volatile semiconductor memory device and memory system

ABSTRACT

A non-volatile semiconductor memory device includes a memory cell array and a control circuit. A control circuit performs an erase operation providing a memory cell with a first threshold voltage level for erasing data of a memory cell, and then perform a plurality of first write operations providing a memory cell with a second threshold voltage level, the second threshold voltage level being higher than the first threshold voltage level and being positive level. When the control circuit receives a first execution instruction from outside during the first write operations, the first execution instruction being for performing first function operation except for the erase operation and the first write operations, the circuit performs the first function operation during the first write operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 13/425,818 filed Mar. 21, 2012,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Application No. 2011-155396 filed Jul. 14, 2011, the entirecontents of each of which are incorporated herein by reference.

FIELD

The embodiments relate to a non-volatile semiconductor memory device anda memory system.

BACKGROUND

In recent years, for a more integrated memory cell, a number ofsemiconductor memory devices (stacked non-volatile semiconductor memorydevices) including three-dimensionally arranged memory cells have beenproposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a non-volatile memory system 100 accordingto a first embodiment.

FIG. 2 is a block diagram of a memory chip 200 according to the firstembodiment.

FIG. 3 is a circuit diagram of a memory cell array 201 according to thefirst embodiment.

FIG. 4 is a schematic perspective view of the memory cell array 201according to the first embodiment.

FIG. 5 is a cross-sectional view of the memory cell array 201 accordingto the first embodiment.

FIG. 6 illustrates a relationship between the threshold voltagedistributions of a memory transistor MTr and data according to the firstembodiment.

FIG. 7 illustrates the issue if the first write operation is notperformed.

FIG. 8 shows the advantage of the first write operation.

FIG. 9 illustrates a state transition diagram according to the firstembodiment.

FIG. 10 is a timing diagram of a first write operation according to thefirst embodiment.

FIG. 11 illustrates an erase status ST according to the firstembodiment.

FIG. 12 is the timing diagram of the first write operation according tothe first embodiment.

FIG. 13 is the timing diagram of the first write operation according toa second embodiment.

FIG. 14 illustrates erase statuses ST(1) and ST(2) according to thesecond embodiment.

FIG. 15 is a timing diagram of the first write operation according tothe second embodiment.

FIG. 16 illustrates a process when after the first write operations tothe memory transistors MTr1 to MTr4 connected to the respectiveword-lines WL1 to WL4 are completed, the first write operation isinterrupted according to a third embodiment.

FIG. 17 is a timing diagram of the first write operation according to afourth embodiment.

FIG. 18 is the timing diagram of the first write operation according tothe fourth embodiment.

FIG. 19 is a timing diagram of the first write operation according to afifth embodiment.

FIG. 20 illustrates a relationship between the threshold voltagedistributions of a memory transistor MTr and data according to anotherembodiment.

DETAILED DESCRIPTION

A non-volatile semiconductor memory device according to an aspectincludes a memory cell array and a control circuit. The memory cellarray includes a plurality of memory cells, and a plurality ofword-lines commonly connected to gates of the memory cells. The controlcircuit is configured to perform an erase operation providing a memorycell with a first threshold voltage level for erasing data of a memorycell, and then perform a plurality of first write operations providing amemory cell with a second threshold voltage level, the second thresholdvoltage level being higher than the first threshold voltage level andbeing positive level. The memory cell array includes a semiconductorsubstrate, a first semiconductor layer, a charge accumulation layer, anda first conductive layer. The first semiconductor layer extends in adirection perpendicular to the semiconductor substrate, and functions asa body of a memory cell. The charge accumulation layer is operative toaccumulate charges. The first conductive layer sandwiches the chargeaccumulation layer with the first semiconductor layer, and functions asagates of the memory cell and a word-line. The control circuit performsthe first write operation to the plurality of memory cells. When thecontrol circuit receives a first execution instruction from outsideduring the first write operations, the first execution instruction beingfor performing first function operation except for the erase operationand the first write operations, the control circuit performs the firstfunction operation during the first write operations.

Referring now to the drawings, non-volatile semiconductor memory devicesaccording to the embodiments will be described.

First Embodiment Configuration

Referring first to FIG. 1, the entire configuration of a non-volatilememory system according to a first embodiment will be described. FIG. 1is a block diagram of anon-volatile memory system 100 according to thefirst embodiment of the present invention.

With reference to FIG. 1, the non-volatile memory system 100 includes aplurality of NAND memory chips 200 (non-volatile semiconductor memorydevices), and a controller 300 for controlling the memory chips 200. Thecontroller 300 operates in response to a control signal from an externalhost computer 400. The controller 300 accesses the memory chips 200 andinstructs them to perform data read, data write, data erase, or thelike.

Referring now to FIG. 2, the specific configuration of each memory chip200 will be described. With reference to FIG. 2, each memory chip 200includes a memory cell array 201 for storing data in a non-volatilemanner, and various circuits 202 to 215 for controlling the memory cellarray 201.

The input/output circuit 202 inputs/outputs a command, an address, anddata via an input/output data I/O. The input/output circuit 202 isconnected to a command register 204, a status register 207, an addressregister 208, and a data register 211, as described below.

A logic circuit 203 receives a chip enable signals /CE1 to /CE4, acommand latch enable signal CLE, an address latch enable signal ALE, awrite-enable signal /WE, a read-enable signal /RE, a write protectsignal /WP, a selection control signal PSL, and other control signals.The logic circuit 203 controls the memory cell array 201 according tothose signals. The logic circuit 203 is connected to the input/outputcircuit 202 and a control circuit 205 as described below. A commandregister 204 decodes a command that is input to the input/output circuit202. The command register 204 is connected to the control circuit 205 asdescribed below.

The control circuit 205 performs the data transfer control and thesequence control of the data write/erase/read. The control circuit 205is connected to status registers 206 and 207, a data register 211, acolumn decoder 212, a sense amplifier 214, and a high voltage generationcircuit 215, as described below.

The status register 206 (which shows RY//BY in FIG. 2 and mayhereinafter be referred to as a first status register) outputs a signalto the Ready/Busy terminal that shows the Ready/Busy state of the memorychip 200. The status register 207 (which may hereinafter be referred toas a second status register) receives a signal from the control circuit205 that shows the state (such as Pass/Fail and Ready/Busy) of thememory chip 200, and outputs the signal to the host computer 400 via theinput/output circuit 202.

The status register 207 includes a region AR for holding an interruptioninformation. The interruption information is information that is inputfrom the control circuit 205. The interruption information is input fromthe control circuit 205 when the first write operations are performed toall memory transistors MTr and an interrupt operation occurs before thefirst write operations are completed. The interruption information willbe described in more detail below.

A row address buffer 209 and a column address buffer 210 receive addressdata via the address register 208 and transfer it. The row addressbuffer 209 is connected to a row decoder 213 as described below. Thecolumn address buffer 210 is connected to a column decoder 212 asdescribed below.

The data register 211 has functions of temporarily holding write data tothe memory cell array 201 and of temporarily holding read data from thememory cell array 201. The write data is transferred to the dataregister 211 via the input/output circuit 202 and a data bus BUS.

The column decoder 212 and the row decoder 213 perform a control ofselecting, according to address data supplied from the row addressbuffer 209 and the column address buffer 210, a word-line WL, a bit-lineBL, a source-line SL, and the like in the memory cell array 201 asdescribed below, and applying desired voltages to them. The senseamplifier 214 senses and amplifies the voltage of the bit-line BL, andreads data from the memory cell array 201.

The high voltage generation circuit 215 generates the desired highvoltage for each operation mode. The high voltage generation circuit 215generates a predetermined high voltage according to an instructionprovided from the control circuit 205. The high voltage generationcircuit 215 is connected to the memory cell array 201, the row decoder213, and the sense amplifier 214.

Referring now to FIG. 3, the circuitry of the memory cell array 201 willbe specifically described.

With reference to FIG. 3, the memory cell array 201 includes m memoryblocks MB(1), . . . , MB(m). Note that all memory blocks MB(1), . . . ,MB(m) may hereinafter be collectively described as a memory block MB.

Each memory block MB includes memory units MU(1, 1) to MU(2, n) arrangedin a matrix of n-rows and 2 columns. The n-rows and 2 columns are merelyan example, and the invention is not limited thereto. Each of the memoryunits MU(1, 1) to MU(2, n) may hereinafter be described merely as amemory unit MU without distinction.

First ends of the memory units MU(1, 1) to MU(2, n) are connected tobit-lines BL(1) to BL(n). Second ends of the memory units MU(1, 1) toMU(2, n) are connected to a source-line SL. The bit-lines BL(1) to BL(n)are provided in the row direction at a predetermined pitch and extend inthe column direction over the memory blocks MB. All bit-lines BL(1), . .. , BL(n) may hereinafter be collectively described as a bit-line BL.

The memory unit MU includes a memory string MS, a source-side selecttransistor SSTr, and a drain-side select transistor SDTr.

With reference to FIG. 3, the memory string MS includes memorytransistors MTr1 to MTr8 (memory cells) connected in series and a backgate transistor BTr. The memory transistors MTr1 to MTr4 and MTr5 toMTr8 are connected in series, respectively. Note that the memorytransistors MTr1 to MTr8 are arranged in the stacking direction, asdescribed below in FIG. 4 and FIG. 5. The back gate transistor BTr isconnected between the memory transistor MTr4 and the memory transistorMTr5.

The memory transistors MTr1 to MTr8 accumulate charge in their chargeaccumulation layers to hold data. The back gate transistor BTr isrendered conductive when at least the memory string MS is selected as anoperation target.

In each of the memory blocks MB(1) to MB(m), gates of the memorytransistors MTr1 to MTr8 arranged in n-rows and 2 columns are commonlyconnected to respective word-lines WL1 to WL8. Gates of the back gatetransistors BTr arranged in n-rows and 2 columns are commonly connectedto a back gate line BG.

The source-side select transistor SSTr has a drain connected to a sourceof the memory string MS. The source-side select transistor SSTr has asource connected to the source-line SL. In each memory block MB, gatesof the n source-side select transistors SSTr aligned in the rowdirection are commonly connected to one source-side select gate lineSGS(1) or SGS(2). Note that the source-side select gate lines SGS(1) andSGS(2) may hereinafter be collectively referred to as a source-sideselect gate line SGS without distinction.

The drain-side select transistor SDTr has a source connected to a drainof the memory string MS. The drain-side select transistor SDTr has adrain connected to the bit-line BL. In each memory block MB, gates ofthe n drain-side select transistors SDTr aligned in the row directionare commonly connected to one drain-side select gate line SGD(1) orSGD(2). Note that the, drain-side select gate lines SGD(1) and SGD(2)may hereinafter be collectively referred to as a drain-side select gateline SGD without distinction.

[Stacked Structure]

With reference to FIG. 4 and FIG. 5, one memory block MB includes a backgate layer 30, a memory layer 40, a select transistor layer 50, and awiring layer 60, which are sequentially stacked on a substrate 20. Theback gate layer 30 functions as the back gate transistors BTr. Thememory layer 40 functions as the memory transistors MTr1 to MTr8. Theselect transistor layer 50 functions as the drain-side selecttransistors SDTr and the source-side select transistors SSTr. The wiringlayer 60 functions as the source-line SL and the bit-line BL.

With reference to FIG. 4 and FIG. 5, the back gate layer 30 includes aback gate conductive layer 31. The back gate conductive layer 31functions as the back gate line BG and as the gates of the back gatetransistors BTr. The back gate conductive layer 31 extendstwo-dimensionally like a plate in the row and column directions parallelto the semiconductor substrate 20. The back gate conductive layer 31 ismade of a material such as polysilicon (poly-Si).

With reference to FIG. 5, the back gate layer 30 includes a memory gateinsulating layer 43 and a joining semiconductor layer 44B. The memorygate insulating layer 43 is provided between the joining semiconductorlayer 44B and the back gate conductive layer 31. The joiningsemiconductor layer 44B functions as a body (channel) of the back gatetransistor BTr. The joining semiconductor layer 44B trims the back gateconductive layer 31. The joining semiconductor layer 44B is formed in agenerally rectangular shape having a longitudinal direction in thecolumn direction when viewed in top plan view. A plurality of joiningsemiconductor layers 44B are formed in a matrix in the row and columndirections in one memory block MB. Each joining semiconductor layer 44Bis made of a material such as polysilicon (poly-Si).

With reference to FIG. 4 and FIG. 5, the memory layer 40 is formed in alayer above the back gate layer 30. The memory layer 40 includes fourword-line conductive layers 41 a to 41 d. The word-line conductive layer41 a functions as the word-line WL4 and as the gates of the memorytransistors MTr4. The word-line conductive layer 41 a also functions asthe word-line WL5 and as the gates of the memory transistors MTr5.Likewise, the word-line conductive layers 41 b to 41 d function as therespective word-lines WL1 to WL3 and as the respective gates of thememory transistors MTr1 to MTr3. The word-line conductive layers 41 b to41 d also function as the respective word-lines WL6 to WL8 and as therespective gates of the memory transistors MTr6 to MTr8.

The word-line conductive layers 41 a to 41 d are stacked with aninterlayer insulating layer 45 disposed therebetween. The word-lineconductive layers 41 a to 41 d reside at a certain pitch in the columndirection and extend in the row direction (a direction perpendicular theplane of FIG. 3) as the longitudinal direction. The word-line conductivelayers 41 a to 41 d are made of a material such as polysilicon(poly-Si).

With reference to FIGS. 4 and 5, the memory layer 40 includes a memorygate insulating layer 43, a columnar semiconductor layer 44A, and adummy semiconductor layer 44D. The memory gate insulating layer 43 isprovided between the columnar semiconductor layer 44A and the word-lineconductive layers 41 a to 41 d. The columnar semiconductor layer 44Afunctions as the bodies (channels) of the memory transistors MTr1 toMTr8. The dummy semiconductor layer 44D does not function as the bodiesof the memory transistors MTr1 to MTr8.

The memory gate insulating layer 43 includes, from the side surfacesides of the word-line conductive layers 41 a to 41 d to a side of thememory columnar semiconductor layer 44A, a block insulating layer 43 a,a charge accumulation layer 43 b, and a tunnel insulating layer 43 c.The charge accumulation layer 43 b is configured to be capable ofaccumulating charge.

The block insulating layer 43 a is formed on the side surfaces of theword-line conductive layers 41 a to 41 d with a predetermined thickness.The charge accumulation layer 43 b is formed on a side surface of theblock insulating layer 43 a with a predetermined thickness. The tunnelinsulating layer 43 c is formed on a side surface of the chargeaccumulation layer 43 b with a predetermined thickness. The blockinsulating layer 43 a and the tunnel insulating layer 43 c are made of amaterial such as silicon dioxide (SiO₂). The charge accumulation layer43 b is made of a material such as silicon nitride (SiN).

The columnar semiconductor layer 44A passes through the word-lineconductive layers 41 a to 41 d and the interlayer insulating layer 45.The columnar semiconductor layer 44A extends in a directionperpendicular to the semiconductor substrate 20. A pair of columnarsemiconductor layers 44A are aligned with the respective end portionvicinities of the joining semiconductor layer 44B in the columndirection. The columnar semiconductor layer 44A is made of a materialsuch as polysilicon (poly-Si). Note that the dummy semiconductor layer44D passes through the word-line conductive layers 41 a to 41 d and theinterlayer insulating layer 45. Under the dummy semiconductor layer 44D,the back gate conductive layer 31 is not provided.

In the above back gate layer 30 and memory layer 40, the pair ofcolumnar semiconductor layers 44A and the joining semiconductor layer44B joining the lower ends of the columnar semiconductor layers 44A forma memory semiconductor layer 44 functioning as a body (channel) of thememory string MS. The memory semiconductor layer 44 is formed in a Ushape when viewed in the row direction.

The above back gate layer 30 has, in other words, a configuration inwhich the back gate conductive layer 31 surrounds the side surface andbottom surface of the joining semiconductor layer 44B via the memorygate insulating layer 43. Further, the above memory layer 40 has, inother words, a configuration in which the word-line conductive layers 41a to 41 d surround the side surface of the columnar semiconductor layer44A via the memory gate insulating layer 43.

With reference to FIG. 4 and FIG. 5, the select transistor layer 50includes a source-side conductive layer 51 a, a drain-side conductivelayer 51 b, and a dummy conductive layer 51 c. The source-sideconductive layer 51 a functions as the source-side select gate line SGSand as the gates of the source-side select transistors SSTr. Thedrain-side conductive layer 51 b functions as the drain-side select gateline SGD and as the gates of the drain-side select transistors SDTr. Thedummy conductive layer 51 c does not function as the source-side selectgate line SGS or the drain-side select gate line SGD.

The source-side conductive layer 51 a is formed in a layer above one ofthe first columnar semiconductor layers 44A included in the memorysemiconductor layer 44. The drain-side conductive layer 51 b is formedin the same layer as the source-side conductive layer 51 a. The layer 51b is also formed in a layer above the other one of the columnarsemiconductor layers 44A included in the memory semiconductor layer 44.The dummy conductive layer 51 c is formed in the same layer as thesource-side conductive layer 51 a and is formed in a portion other thanthe portion over the columnar semiconductor layer 44A. More than onesource-side conductive layers 51 a, drain-side conductive layers 51 b,and dummy conductive layers 51 c are provided at a predetermined pitchin the column direction and extend in the row direction. The source-sideconductive layer 51 a and the drain-side conductive layer 51 b are madeof a material such as polysilicon (poly-Si).

With reference to FIG. 5, the select transistor layer includes asource-side gate insulating layer 53 a, a source-side columnarsemiconductor layer 54 a, a drain-side gate insulating layer 53 b, adrain-side columnar semiconductor layer 54 b, and a dummy semiconductorlayer 54D. The source-side columnar semiconductor layer 54 a functionsas a body (channel) of the source-side select transistor SSTr. Thedrain-side columnar semiconductor layer 54 b functions as a body(channel) of the drain-side select transistor SDTr.

The source-side gate insulating layer 53 a is provided between thesource-side conductive layer 51 a and the source-side columnarsemiconductor layer 54 a. The source-side columnar semiconductor layer54 a passes through the source-side conductive layer 51 a. Thesource-side columnar semiconductor layer 54 a is connected to a sidesurface of the source-side gate insulating layer 53 a and a top surfaceof one of the pair of columnar semiconductor layers 44A. The source-sidecolumnar semiconductor layer 54 a is formed in a columnar shapeextending in a direction perpendicular to the semiconductor substrate20. The source-side columnar semiconductor layer 54 a is made of amaterial such as polysilicon (poly-Si).

The drain-side gate insulating layer 53 b is provided between thedrain-side conductive layer 51 b and the drain-side columnarsemiconductor layer 54 b. The drain-side columnar semiconductor layer 54b passes through the drain-side conductive layer 51 b. The drain-sidecolumnar semiconductor layer 54 b is connected to a side surface of thedrain-side gate insulating layer 53 b and atop surface of the other oneof the pair of columnar semiconductor layers 44A. The drain-sidecolumnar semiconductor layer layer 54 b is formed in a columnar shapeextending in a direction perpendicular to the semiconductor substrate20. The drain-side columnar semiconductor layer 54 b is made of amaterial such as polysilicon (poly-Si).

The dummy semiconductor layer 54D passes through the dummy conductivelayer 51 c. The dummy semiconductor layer 54D is formed in an I shape. Abottom surface of the dummy semiconductor layer 54D is in contact with atop surface of the dummy semiconductor layer 44D.

The wiring layer 60 includes a source-line layer 61, a bit-line layer62, and a plug layer 63. The source-line layer 61 functions as thesource-line SL. The bit-line layer 62 functions as the bit-line BL.

The source-line layer 61 is in contact with a top surface of thesource-side columnar semiconductor layer 54 a and extends in the rowdirection. The bit-line layer 62 is in contact with a top surface of thedrain-side columnar semiconductor layer 54 b via the plug layer 63 andextends in the column direction. The source-line layer 61, the bit-linelayer 62, and the plug layer 63 are made of metal material such astungsten.

[Operations]

A description is now given of an erase operation, a first writeoperation, and a second write operation according to the firstembodiment. For convenience of description, a 2-bit/cell is described asan example. Specifically, threshold voltage distributions of the memorytransistor MTr may include one negative distribution (E) and fourpositive distributions (EP, A, B, and C). FIG. 6 illustrates arelationship between the 2-bit four-level data (data “11,” “10,” “01,”and “00”) stored in the memory transistor MTr and the threshold voltagedistributions of the memory transistor MTr. Here, data “11” (E and EP)indicates an erased state and data “10,” “01,” “00” (A, B, and C)indicate a write state. A lower limit of the threshold voltagedistribution E has a negative value. The lower limits of the thresholdvoltage distributions EP, A, B, and C have positive values. Thethreshold voltage distributions EP, A, B, and C are arranged in thepositive direction at a predetermined margin.

The erase operation causes holes to be trapped in the chargeaccumulation layer 43 b of the memory transistor MTr, thereby moving thethreshold voltage distributions EP, A, B, and C in the negativedirection to be set to the threshold voltage distribution E. The firstwrite operation is performed after the erase operation. The first writeoperation causes electrons to be trapped in the charge accumulationlayer 43 b of the memory transistor MTr, thereby moving the thresholdvoltage distribution E in the positive direction to be set to thethreshold voltage distribution EP.

The second write operation causes electrons to be trapped in the chargeaccumulation layer 43 b of the memory transistor MTr, and moves,depending on the trapped amount, the threshold voltage distribution E orEP in the positive direction to be set to the threshold voltagedistribution A, B, or C (A<B<C).

The reason for performing the first write operation will now bedescribed. First, referring to FIG. 7, the issue if the first writeoperation is not performed will be described. The charge accumulationlayer 43 b is continuous through the memory transistors MTr1 to MTr8.Accordingly, in this case, if one memory transistor MTr has, forexample, a threshold voltage distribution A and another memorytransistor MTr adjacent to that memory transistor MTr has a thresholdvoltage distribution E, charges (electrons, holes) move between theadjacent memory transistors MTr1 to MTr8 over time. Specifically, withreference to FIG. 7, it is assumed that after the erase operation isperformed, the first write operation is not performed, and the secondwrite operation is performed only to the selected memory transistorMTr2, and other non-selected memory transistors MTr1 and MTr3 to MTr8remain in the erased state. In this case, the charge accumulation layer43 b of the selected memory transistor MTr2 is in a state in whichelectrons are trapped, and the charge accumulation layer 43 b of theother non-selected memory transistors MTr1 and MTr3 to MTr8 is in astate in which holes are trapped. Thus, between the adjacent memorytransistors MTr1, MTr2, and MTr3, charges (electrons, holes) mayrecombine, thereby losing data of the selected memory transistor MTr2.

Therefore, the non-volatile semiconductor memory device according to thefirst embodiment performs the first write operation after the eraseoperation. Thus, with reference to FIG. 8, the charge accumulation layer43 b of the memory transistors MTr1 to MTr8 is in a state in whichelectrons are trapped regardless of stored data. Therefore, the firstembodiment may reduce the charge recombination between the adjacentmemory transistors MTr1 to MTr8. As a result, the data loss(degradation) may be reduced.

The first write operation described above is performed more than once bythe control circuit 205. With reference to FIG. 8, the first writeoperation is performed once for each of the memory transistors MTr1 tothe memory transistors MTr8 commonly connected to the respectiveword-lines WL1 to WL8. The first write operation is performed in theorder of the memory transistors MTr1 to MTr8.

Referring now to FIG. 9, a schematic operation of the control circuit205 will be described. After the erase operation, the control circuit205 performs the first write operations in the idle state (idling) inwhich various operations such as the second write operation and the readoperation are not performed. Then, when an execution command of thesecond write operation or the read operation (execution command for anoperation except for the erase operation and the first write operation)is received during the first write operations, the control circuit 205performs the second write operation or the read operation (interruptoperation) during the first write operations. Because of the interruptoperation, the first embodiment may rapidly perform the second writeoperation and the read operation even during the first write operations.

With reference to FIG. 9, the control circuit 205 is typically in theidle state (S101) and receives an erase command CMDe from the controller300. Here, the erase command CMDe in the first embodiment is a commandfor performing the erase operation and then successively performing thefirst write operations. Therefore, when the control circuit 205 receivesthe erase command CMDe in step S101, it first performs the eraseoperation (S102), and then performs the successive first writeoperations (S103 and S104).

Specifically, in step S103, the control circuit 205 checks whether ornot there is an interruption command CMDb for interrupting the firstwrite operations. Here, when the interruption command CMDb is notpresent, the control circuit 205 performs the first write operation to,for example, the memory transistors MTr1 commonly connected to oneword-line WL1 (S104). Then, it is checked again whether the interruptioncommand CMDb is present or not (S103). When the interruption commandCMDb is not present, the first write operation is performed to thememory transistors MTr2 commonly connected to the one word-line WL2(S104). Then steps S103 and S104 are repeated, and when it is determinedthat the first write operations are completed to all memory transistorsMTr1 to MTr8, the control circuit 205 returns to the idle state (S101).

In the above step S103, when the interruption command CMDb is present,then the control circuit 205 determines whether or not the otherexecution command (read command CMDr or write command CMDw), or a resumecommand CMDs is present (S105). When receiving the other executioncommand CMDr or CMDw, the control circuit 205 performs that operation(S106), and returns to the process in step S105. In step S105, thecontrol circuit 205 resumes, when it receives the resume command CMDs,the first write operation in response to the resume command CMDs (S104).

Here, it is possible to consider, as a comparative example, a process inwhich immediately after the erase operation or the second writeoperation, the first write operations are intermittently performedpreferentially than the other operations. In the process in thecomparative example, however, the other operations requested in thefirst write operations are performed after the first write operationsare completed. Further, the memory cell array 201 in this embodimentincludes three-dimensionally arranged memory transistors MTr1 to MTr8,and thus it has a larger capacity than the conventional memory cellarray including two-dimensionally arranged memory transistors. Thus,adoption of the process of the comparative example in this embodimentwill dramatically increase the delay time. In this embodiment,therefore, the process shown in FIG. 9 is performed to rapidly performthe second write operation and the read operation even during the firstwrite operations.

Referring now to FIG. 10, an example is described in which the eraseoperation and the first write operations are performed without aninterruption. With reference to FIG. 10, the control circuit 205receives, from the controller 300, an erase address input commandCMDeadd and an address data ADDe. Then, the control circuit 205 receivesthe erase command CMDe. Then, the control circuit 205 performs the eraseoperation to the memory transistor MTr in the address assigned by theerase command CMDe and address data ADDe (Erase). The memory chip 200enters the busy state. Then, continuously after the erase operation, thecontrol circuit 205 successively performs the first write operations.After the first write operations are completed and the memory chip 200is in a ready state, the control circuit 205 receives a status commandCMDst and outputs the erase status ST to the controller 300 via thestatus register 207. The controller 300 holds the erase status ST.

The erase status ST is indicated by, for example, 3-bit data. FIG. 11illustrates the correspondence between the configuration of the erasestatus ST and I/O0 to I/O7.

The first bit data (corresponding to I/O0) of the erase status ST isdata indicating whether the erase operation passes or fails. The secondbit data (corresponding to I/O1) is data indicating whether the firstwrite operations are completed or not to all memory cell transistorsMTr1 to MTr8 connected to all word-lines WL1 to WL8. Further, the thirdbit data (corresponding to I/O2) is data indicating whether the firstwrite operations to all memory transistors MTr1 to MTr8 pass or fail.For example, even if the first write operation fails only to one memorytransistor MTr1 (only the memory transistor MTr1 is defective), datacorresponding to I/O2 “fails.” Therefore, data corresponding to I/O2 mayidentify the defective memory block MB.

Referring now to FIG. 12, an example is described in which the readoperation or the like interrupts the first write operations and isperformed. FIG. 12 shows an example in which after the first writeoperations in the memory transistors MTr1 to MTr4 connected to therespective word-lines WL1 to WL4 are completed, the read operation isperformed. With reference to FIG. 12, like FIG. 10, the control circuit205 performs the erase operation (Erase), and then successively performsthe first write operations (Erase, EP Prog for MTr1-4). When, during thefirst write operations, the host computer 400 has an access regardingthe read operation, the control circuit 205 receives the interruptioncommand CMDb from the controller 300. Then, the control circuit 205interrupts, in response to the interruption command CMDb, the successivefirst write operations. Then, the control circuit 205 receives thestatus command CMDst. In response to the status command CMDst, thecontrol circuit 205 outputs the erase status ST to the controller 300.In so doing, along with the output of the erase status ST, the controlcircuit 205 stores the interruption information in the region AR in thestatus register 207 in the memory chip 200 (see FIG. 2). Theinterruption information is related to the state in which the firstwrite operations are interrupted. Here, the interruption informationindicates that the first write operations are performed to the memorytransistors MTr1 to MTr4, and the first write operations are notperformed to the memory transistors MTr5 to MTr8.

Then, the control circuit 205 receives a read address input commandCMDradd and an address data ADDr. Then, the control circuit 205 receivesthe read command CMDr, and performs the read operation to the memorytransistor MTr in the address assigned by address data ADDr (Read).Then, the control circuit 205 outputs read data Data.

Then, the control circuit 205 receives the resume command CMDs from thecontroller 300, thereby resuming the first write operations to theremaining memory transistors MTr5 to MTr8 to which the first writeoperations are not performed (EP Prog for MTr5-8). Here, the controlcircuit 205 reads the interruption information from the status register207. According to the interruption information, the control circuit 205resumes the first write operations from the memory transistor MTr5.

As described above, this embodiment may provide a non-volatilesemiconductor memory device that may have improved reliability of dataheld in the memory transistor (the memory cell).

The non-volatile semiconductor memory device according to thisembodiment is discussed using, as a comparative example, a non-volatilesemiconductor memory device in which the erase operation is continuouslyfollowed by the first write operations and then the read operation andthe second write operation may be performed.

In the comparative example, the read operation and the second writeoperation are performed after the first write operations are completed.In other words, this increases the total time of the erase operation andthe first write operations, thereby having to wait for the next readoperation and the second write operation for a long period of time.

However, the non-volatile semiconductor memory device according to thisembodiment performs the first write operation during the idle state. Inother words, when the read operation and the second write operation arenot performed, the erase operation is followed by the first writeoperations. When the first write operations are interrupted by the readoperation or the second write operation, the interrupt operation isprioritized. Then, when the interrupt operation is completed and theidle state occurs, the first write operations are resumed.

As a result, the next read operation and second write operation may beperformed after the erase operation, thereby not having to wait for theexecution time of the first write operations. The non-volatilesemiconductor memory device according to this embodiment may perform theread operation and the second write operation more quickly after theerase operation than the device in the comparative example. As a result,the non-volatile semiconductor memory device according to thisembodiment may have improved performance compared to the device in thecomparative example.

Second Embodiment

A non-volatile memory system according to a second embodiment will nowbe described. The configuration of the second embodiment is similar tothat of the first embodiment and thus its description is omitted here.As described below, the second embodiment has different first writeoperations from the first embodiment.

Referring first to FIG. 13, an example is described in which the eraseoperation and the first write operations are performed without aninterruption. Here, in the above first embodiment, in response to onestatus command CMDst, one erase status ST is output to the controller300. Because, however, the erase status ST does not include information(interruption information) indicating whether the first write operationis completed or not for each memory transistor MTr, the controller 300may not identify the state where the first write operations areinterrupted. In contrast, in the second embodiment, with reference toFIG. 13, in response to one status command CMDst, a plurality of erasestatuses ST(1), (2), . . . are output to the controller 300. The firsterase status ST(1) indicates whether the erase operation passes orfails. Second or subsequent erase statuses ST(2), (3), . . . , eachinclude information (interruption information) indicating whether thefirst write operations to the memory transistors MTr1, MTr2, . . . ,connected to the respective word-lines WL1, WL2, . . . , are completedor not, and information indicating whether each first write operationpasses or fails. Because this embodiment provides 8 word-lines WL1 toWL8, 9 erase statuses (1) to (9) are output to and stored in thecontroller 300. Therefore, these erase statuses ST(1), . . . , (9) mayallow the controller 300 to identify the state where the first writeoperations is interrupted and identify the defective memory transistorMTr.

Referring now to FIG. 14, an example of the erase statuses ST(1) andST(2) will be described. The erase status ST(1) is indicated by, forexample, 1-bit data, and the erase status ST(2) is indicated by, forexample, 2-bit data. FIG. 14 illustrates the correspondence between theconfigurations of the erase statuses ST(1) and ST(2) and I/O0 to I/O7.

The first bit data (corresponding to I/O0) of the erase status ST(1) isdata indicating whether the erase operation passes or fails. The firstbit data (corresponding to I/O0) of the erase status ST(2) is dataindicating whether the first write operation is completed or not to thememory transistor MTr1. And, the second bit data (corresponding to I/O1)of the erase status ST(2) is data indicating whether the first writeoperation to the memory transistor MTr1 passes or fails. Note that theerase statuses ST(3) to ST(9) are only different from the erase statusST(2) in that the target memory transistor MTr is different, and thustheir detailed description is omitted here.

Referring now to FIG. 15, an example is described in which the readoperation or the like interrupts the first write operations and isperformed. FIG. 15 shows an example in which after the first writeoperations to the memory transistors MTr1 to MTr4 connected to therespective word-lines WL1 to WL4 are completed, the read operation isperformed. With reference to FIG. 15, after the read operation Read, thecontrol circuit 205 receives, from the controller 300, the resumecommand CMDs for resuming the first write operation, and an addressAdds, and then resumes the first write operations from the memorytransistor MTr5 assigned by the address Adds. Here, as described above,the controller 300 stores, according to the erase statuses ST(1), . . ., ST(9), whether the first write operation is completed or not (theinterruption information) for each of the memory transistors MTr1 toMTr8. Thus, the controller 300 may generate the address Adds when thefirst write operations are resumed.

As described above, in the second embodiment, the interruptioninformation of the first write operations is held in the controller 300according to the erase statuses ST(1) to ST(9). Thus, in the secondembodiment, unlike the first embodiment, it is not necessary to hold theinterruption information in the memory chip 200 (the status register207).

Note that the non-volatile semiconductor memory device in the secondembodiment may provide a similar advantage to that in the firstembodiment.

Third Embodiment

A non-volatile memory system according to a third embodiment will now bedescribed. The configuration of the third embodiment is similar to thatof the first embodiment and thus its description is omitted here. Asdescribed below, the third embodiment has different first writeoperations from the first embodiment.

FIG. 16 illustrates a process when the first write operation isinterrupted, after the first write operations to the memory transistorsMTr1 to MTr4 connected to the respective word-lines WL1 to WL4 arecompleted, in the third embodiment. In the first embodiment, when thefirst write operations are completed up to the memory transistor MTr4,the first write operation is resumed from the memory transistor MTr5. Incontrast, in the third embodiment, with reference to FIG. 16, the firstwrite operation is resumed from the memory transistor MTr4. Further, inthe third embodiment, when resuming, the first write operation to thememory transistor MTr4 is performed after a verify operation determiningwhether or not the threshold of the memory transistor MTr4 is set to apredetermined value.

The reason for resuming the first write operation as shown in FIG. 16will now be described. As described above, if after the first writeoperations to the memory transistors MTr1 to MTr4 are completed, thefirst write operation is interrupted, the charge accumulation layer 43 bof the memory transistors MTr1 to MTr4 is in the state in whichelectrons are trapped. In contrast, the charge accumulation layer 43 bof the memory transistors MTr5 to MTr8 remains in the state in whichholes are trapped. Thus, charges (electrons or holes) of the memorytransistors MTr4 and MTr5 may recombine, thereby reducing the thresholdvoltage of the memory transistor MTr4. Therefore, the third embodimentresumes the first write operation from the memory transistor MTr4,thereby suppressing the threshold voltage reduction of the memorytransistor MTr4. Therefore, the longer time it takes before the firstwrite operation is resumed, the more effective the third embodiment is.

Note that the non-volatile semiconductor memory device in the thirdembodiment may also provide a similar advantage to that in the firstembodiment.

Fourth Embodiment

A non-volatile memory system according to a fourth embodiment will nowbe described. The configuration of the fourth embodiment is similar tothat of the first embodiment and thus its description is omitted here.As described below, the fourth embodiment has different first writeoperations from the first embodiment.

Referring first to FIG. 17, an example is described in which the eraseoperation and the first write operation are performed without aninterruption. With reference to FIG. 17, in the fourth embodiment, thecontrol circuit 205 receives, unlike the first embodiment, a first writecommand CMDep independently from the erase command CMDe. In the fourthembodiment, the erase command CMDe is a command for performing the eraseoperation, and the first write command CMDep is a command forsuccessively performing the first write operations. In response to thefirst write command CMDep, the control circuit 205 successively performsthe first write operations. After all first write operations arecompleted, the control circuit 205 receives the status command CMDst. Inresponse to the status command CMDst, the control circuit 205 outputsthe erase status ST.

Referring now to FIG. 18, an example is described in which the readoperation or the like interrupts the first write operations and isperformed. FIG. 18 shows an example in which after the first writeoperations to the memory transistors MTr1 to MTr4 connected to therespective word-lines WL1 to WL4 are completed, the read operation isperformed. With reference to FIG. 18, after the read operation Read, thecontrol circuit 205 receives, from the controller 300, a resume commandCMDs for resuming the first write operations, and resumes the firstwrite operations from the memory transistor MTr5.

Note that the non-volatile semiconductor memory device in the fourthembodiment may also provide a similar advantage to that in the firstembodiment.

Fifth Embodiment

A non-volatile memory system according to a fifth embodiment will now bedescribed. The configuration of the fifth embodiment is similar to thatof the first embodiment and thus its description is omitted here. Asdescribed below, the fifth embodiment has different first writeoperations from the first embodiment.

With reference to FIG. 19, in the fifth embodiment, the control circuit205 receives inputs of a plurality of first write commands CMDep(1) toCMDep(8) for performing one first write operation to the respectivememory transistors MTr1 to MTr8. Then, the control circuit 205 performs,according to the first write commands CMDep (1) to CMDep (8), the firstwrite operations to the respective memory transistors MTr1 to MTr8.Then, the control circuit 205 receives, after performing the first writeoperations to the memory transistors MTr1 to MTr8, the status commandCMDst. In response to the status command CMDst, the control circuit 205outputs the erase status ST′ to the controller 300. The erase status ST′includes information indicating whether the first write operations arecompleted or not for the memory transistors MTr1 to MTr8.

In the above fifth embodiment, the first write operations to the memorytransistors MTr1 to MTr8 are performed by the respective different firstwrite commands CMDep(1) to CMDep(8). Therefore, the control circuit 205receives, during the first write operations, the read command CMDr andthe write command CMDw, in response to which the control circuit 205 mayperform the read operation and the second write operation. Further,because the controller 300 receives the erase status ST′ for each firstwrite operation, the controller 300 may identify the memory transistorMTr to which the first write operation is completed.

Here, in the above first to fourth embodiments, the controller 300 needsto issue the interruption command CMDb and the resume command CMDs. Incontrast, the fifth embodiment does not need the interruption commandCMDb and the resume command CMDs. Therefore, the fifth embodiment mayprovide shorter processing time than the first to fourth embodiments.

Note that the non-volatile semiconductor memory device in the fifthembodiment may also provide a similar advantage to that in the firstembodiment.

[Others]

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

For example, in the above embodiments, the first write operation isperformed to a memory transistor MTr that stores four-level data.However, the first write operation may also be performed to a memorytransistor MTr that stores binary data as shown in FIG. 20.

FIG. 20 shows a relationship between 1-bit binary data (data “1” and“0”) stored in the memory transistor MTr and threshold voltagedistributions of the memory transistor MTr. Here, data “1” (E and EP)indicates the erased state, and data “0” (A) indicates the write state.A lower limit of the threshold voltage distribution E has a negativevalue. The lower limits of the threshold voltage distributions EP and Ahave positive values. The threshold voltage distributions EP and A arearranged in the positive direction at a predetermined margin.

With reference to FIG. 20, the erase operation causes holes to betrapped in the charge accumulation layer 43 b of the memory transistorMTr, thereby moving the threshold voltage distributions EP and A in thenegative direction to be set to the threshold voltage distribution E.The first write operation causes electrons to be trapped in the chargeaccumulation layer 43 b of the memory transistor MTr, thereby moving thethreshold voltage distribution E in the positive direction to be set tothe threshold voltage distribution EP. The second write operation causeselectrons to be trapped in the charge accumulation layer 43 b of thememory transistor MTr, and move, depending on the trapped amount, thethreshold voltage distribution E or EP in the positive direction to beset to the threshold voltage distribution A.

What is claimed is:
 1. A non-volatile semiconductor memory devicecomprising: a memory cell array comprising a plurality of memory cells,and a plurality of word-lines connected to gates of the memory cells;and a control circuit configured to perform an erase operation providinga memory cell with a first threshold voltage level for erasing data of amemory cell, and then perform a plurality of first write operationsproviding a memory cell with a second threshold voltage level, thesecond threshold voltage level being higher than the first thresholdvoltage level and being positive level, the memory cell arraycomprising: a semiconductor substrate; a first semiconductor layerextending in a direction perpendicular to the semiconductor substrate,and functioning as a body of a memory cell; a charge accumulation layeroperative to accumulate charges; and a first conductive layersandwiching the charge accumulation layer with the first semiconductorlayer, and functioning as a gate of the memory cell and a word-line, thecontrol circuit performing the first write operation to the plurality ofmemory cells, and when the control circuit receives a first executioninstruction from outside during the first write operations, the firstexecution instruction being for performing a first function operationexcept for the erase operation and the first write operations, thecontrol circuit performs the first function operation during the firstwrite operations.